This invention relates to diesel fuel for an automotive diesel engine operated in combination with a ceramic trap for removing carbonaceous particulates from exhaust gases, which trap is periodically regenerated by burnoff of the collected material. More particularly, this invention relates to diesel fuel containing a cerium naphthenate additive and a manganese dioxide additive for introducing the metals into the particulates in a combination that is particularly effective to improve trap regenerability.
It has been proposed to filter exhaust gases from an automotive diesel engine to remove entrained carbonaceous particulates that are byproducts of the diesel combustion process and thereby reduce emissions of said particulates into the atmosphere. For this purpose, a ceramic trap is incorporated into the exhaust system onboard an automotive vehicle. The accumulation of particulate material within the trap increases the exhaust backpressure, which adversely affects engine performance. To reduce the backpressure, the collected material is periodically ignited and combusted, which regenerates the trap. Before igniting, it is necessary that the quantity of material be sufficient to sustain combustion. In general, increasing the quantity of accumulated material facilitates sustained combusion, but sacrifices engine performance because of increased exhaust backpressure. In addition, a heavier loading tends to produce a higher burnoff temperature and may damage the trap. Therefore, it is desired to reduce the loading required to sustain combustion and regenerate the trap.
It is known that the combustion of diesel particulates may be catalyzed by a metal such as manganese or lead. A compound of the metal is typically added to the fuel. During the engine combustion, the metal becomes dispersed into the particulates. The metal tends to reduce the ignition temperature and thereby promotes sustained combustion that regenerates the trap. Cerium has also been tested as a diesel fuel additive and was believed to behave similarly in reducing the particulate ignition temperature, although with different degrees of effectiveness. However, I have now found that addition of a combination of particular compounds of manganese and cerium substantially improves trap regenerability.
Therefore, it is an object of this invention to provide an improved diesel fuel for operating a diesel engine in combination with a trap for filtering particulates from exhaust gases, which fuel comprises a combination of a cerium additive and a manganese additive in amounts sufficient to enhance combustion of accumulated particulates and thereby promote regeneration of the trap. A surprising feature of this invention is that the combination of cerium and manganese additives decreases the quantity of particulate material required to sustain combustion after ignition to regenerate the trap. This reduces the maximum loading on the trap, thereby reducing the maximum exhaust pressure resulting therefrom and improving engine performance.